Most of 550 between Bernalillo and Cuba is Pueblo land. There is a small section of BLM immediately before and immediately after San Ysidro, but I can't think of any good roads in either of those areas that would get you a little ways off of 550 where you'd be comfortable pitching a tent. But I never looked that closely, so there may be one there.
There is the Cabezon graded dirt road about 2.5 miles south of San Ysidro, where you would need to drive about 4 miles to get to BLM, and then there are some areas in there that aren't developed campgrounds, but it would probably be fine and secluded enough to pitch a tent.
After San Ysidro, you'd have to drive about 26 miles to get to the next BLM. I've probably driven through that area a couple hundred times, but I've never paid close enough attention to be able to say whether there is any good places to pitch a tent that would be convenient to 550. I do know there are stretches between there and Cuba where Continental Divide Trail thru hikers often camp. I just don't know exactly where.